The present invention relates to a microfilm retrieval device which can precisely position a frame of a microfilm at a desired position by instantly suspending the conveyance of the microfilm for retrieval.
FIG. 1 is a schematic view of a prior art microfilm retrieval device, to which the present invention is applicable. In the figure, a cartridge 41 around which a roll of microfilm 1 is wound is housed in a cartridge box 40 at the feeding side. The microfilm 1 which is automatically rewound from the cartridge 41 is automatically wound around an automatic reel 42 at a winding side through a retrieval section 50. The microfilm 1 is conveyed at a high speed by DC motors MH1 and MH2 for high speed conveyance which rotate the cartridge 41 and the automatic reel 42 respectively. At the same time, the microfilm 1 is conveyed at a low speed in a direction of an arrow M or N in the drawing by a conveyor mechanism 2 comprising a DC motor ML for low speed conveyance which is provided between the cartridge 41 and the automatic reel 42 and which can rotate in both directions one of a pair of nip rollers 3 for the low speed conveyance which is provided to hold the microfilm 1 therebetween. The light is irradiated onto the microfilm 1 from a light source 51 of the retrieval section 50, and the light transmitted through the microfilm 1 is converged by a lens system 52, and is transmitted to a reader/printer section (not shown) as image data of the microfilm 1 to position a desired frame and suspend the conveyance. In such a microfilm retrieval device, blip marks 6 are conventionally provided on each frame on the microfilm 1 in order to detect the necessary frames as shown in FIG. 2. The blip marks 6 are detected on the microfilm 1 at the retrieval section 50 by a sensor such as a photodiode (not shown). When the blip mark of the desired frame is detected, a stop signal is generated from a controller section (not shown) to suspend the conveyance of the microfilm 1. Detection and positioning of each frame are carried out in this manner.
At the high speed retrieval, the microfilm 1 is conveyed by the DC motors MH1 and MH2 while the DC motor ML used for the conveyor mechanism 2 is connected/disconnected to and from the nip rollers 3. When disconnected, the nip rollers 3 become freely slidable and are moved to rotate with the friction against the microfilm 1 which is being conveyed therebetween. After the microfilm 1 is conveyed at the high speed and the target image frame approaches to the retrieval section 50, the power source is switched to the DC motor ML for low conveyance and the target image frame is retrieved. However, even though it may be conveyed at the low speed, the DC motor ML for the low speed conveyance cannot immediately stop when receiving the stop signal due to fluctuation in loads, inertia caused by rotating parts deviation and the time lag in response by an electromagnetic clutch. The desired image frame of the microfilm 1 cannot consequently be positioned at the center of the target position. The prior art retrieval device is therefore defective in that the image frame has to be manually adjusted positionwise each time, which is time-consuming as well as imposing extra burden on the operators.